The present invention relates to cable protection assemblies for flexible cables which extend along a production string in undersea oil wells and the like.
The completion of an oil well is typically carried out by lowering a production tube to a blow-out preventer located on the seabed, and on down through the blow-out preventer to the reservoir. The blow-out preventer includes, among other things, several pipe rams with elastic valve elements. Consecutive lengths of production tube, screwed together to form a well path, are lowered vertically down through the blow-out preventer. At annular space is thereby produced between the production tube and the valve element. Flexible electrical and hydraulic cables extend longitudinally along the side of the production tube and down to connected tools or measuring instruments down in the well (which may be a production, injection or observation well).
It is generally necessary to attach the cables to the production tube. In principle, this can be done by simple straps or ties spaced at suitable intervals along the production tube. However, it may be desirable to provide more complicated attachment means. Thus U.S. Pat. No. 2,858,093 (Knoll/Maihak AG) describes a protective device or clip consisting of a cap which covers an exposed portion of the cable where the cable passes over an enlargement such as a joint in the pipe string; the device is secured by clamps to the pipe string. U.S. Pat. No. 4,004,326 (Beavers/Borg Warner) describes a sleeve divided longitudinally into two parts which are screwed around a pipe string; in one of the sleeve""s outer walls there is a recess in which the cable is securely clamped. U.S. Pat. No. 5,667,009 (Moore) concerns the insulation of live cables when they are passed through a wellhead.
During procedures such as pressure testing of the annular space, the valve element in the pipe ram is pressurized with the result that it is expanded, enveloping the production tube, and only when the production tube is completely enveloped can pressure testing be performed. There is therefore a risk of compression damage to the cableways passing alongside the production tube. The cable attachments described above either do not provide protection for the cables or prevent the valve element from forming a pressure-tight seal against the production tube.
The object of the invention is to provide a means for effectively protecting cables on a production pipe during such pressure testing.
According to the invention there is provided a cable protection assembly for flexible electrical and/or hydraulic cables which extend along a production string which communicates with a well through a blow-out preventer located on the seabed, the blow-out preventer including a pipe ram with an elastic valve element which, when pressurized, expands to envelop the production string,
characterized in that the protection assembly comprises:
a core pipe with a threaded connection at each end for connection in the production pipe,
a sleeve around the core pipe and having upper and lower end closure elements welded to the core pipe, each end closure element including at least one cable hole having a pressure-tight coupling for coupling to a cable, and
at least one link pipe extending through the longitudinal annular space formed between the core pipe and the protective sleeve and connecting a pair of cable holes, one in each end element.
In the preferred arrangement, a sleeve-shaped body envelops an allotted length of a core tube or pipe which is connected in and forms part of the production tube, so producing a longitudinal annulus in the area in which pressure testing requires to be conducted. This annulus is closed in a pressure-tight manner by means of end elements with associated supporting and protective brackets. Several link pipe connections are passed as required through this annulus extending between the two end elements. Connecting passages are provided through the end elements with the link pipes connected to them from inside the annulus and such that hydraulic cables can be connected to them and electrical cables can be passed through them, in a pressure-tight manner in both cases. In order to prevent collapse of the sleeve-shaped body when it is exposed to mechanical forces from the pipe ram""s valve element, a number of support rings are mounted inside it, with a corresponding number of holes corresponding to the said pipe connections. The longitudinal cable connections through the link pipes are thereby secured against compression damage.
A blow-out preventer including a protective sleeve in accordance with the invention will now be described, by way of example, with reference to the drawings, in which: